We appreciate the opportunity to respond to the discussion by Nasdala (2009) concerning our interpretation of infrared spectra used to investigate the change in the structure of Pb-irradiated zircon as a function of increasing flux (Zhang et al. 2008a, 2008b). Nasdala is correct in cautioning experimentalists to carefully match the analytical technique to the expected irradiation damage profile to optimally probe the irradiation effects, and in fact, this point was emphasized by Ewing et al. (2003) in a review of radiation effects in zircon. However, Nasdala’s discussion fails to fully appreciate three important points. (1) There is a difference between in situ irradiations of TEM samples that must be electron transparent, ~200 nm thick, as were completed by Weber et al. (1994), and more bulk-like irradiations that were completed in the Zhang et al. (2008a, 2008b) studies. (2) The particle-solid interactions change along the path of an implanted ion, that is the distribution and nature of the damage changes with depth as the ion loses energy, resulting in the greatest number of ballistic interactions near the end of the particle trajectory (see Fig. 1 of Ewing et al. 2003). (3) In comparing natural zircon damaged by alpha-decay events with ion-irradiated zircon, one must be aware that the recoil nucleus and the alpha particle cause different types of damage, and the use of the Pb-implantation experiment is meant to simulate only the alpha-recoil damage.

Pb-implanted vs. metamict zircon

Nasdala disagrees with our conclusion that there is a difference between Pb-implanted and metamict zircon. Although similarities are found between metamict zircon and Pb-irradiated (as well as Au-irradiated) zircon, it has been observed that ion irradiation does not cause the same extent of change in band frequency and width as those seen in metamict zircon, especially for the Raman v3 band (Zhang et …